The functionality of many computing systems relies on effective display of information using a display. More recently, the display has also been used as a direct input device. For instance, a display might be equipped with touch sense resistive and/or capacitive arrays to detect a portion of the display being contacted.
Displays may also be equipped with a camera system that is positioned at some distance behind the display. The camera focuses on objects closer to the display to allow for visual input to the computing system by having the computer visually detect objects interacting with the display. Such “vision capture” technology relies on the presence of some distance between the display panel and the camera system placed behind the display. These vision capture systems are thus quite large, but are quite acceptable for many applications such as projection systems in which the thickness of the display is not critical.
Recently, technology has been made available that allows for high quality displays to be quite thin. For instance, Liquid Crystal Display (LCD) displays are presently in widespread use. Nevertheless, a variety of other thin screen technologies have been developed. One more recent approach is to use a planar light guide as a display.
The planar light guide may be, for example, a sheet of glass or other translucent material such as acrylic. A projector is situated at one end of the planar light guide and projects an image into one end of the sheet. The sheet has an area of a thickness that allows the image to propagate and expand. The thickness may be uniform, vary linearly, or vary non-linearly, so long as the image is permitted to propagate. The image propagates due to total internal reflectance so long as the angle of reflection is below a critical angle defined by the index of refraction of the light guide material and the index of refraction of the ambient surrounding material.
The expanded image is then received into a region of non-uniform thickness, comparable to a wedge shape, where the thickness of the material is gradually reduced. As the image progresses into the wedge, the angle of reflection becomes sharper and sharper approaching the critical angle until total internal reflection can no longer be maintained when the angle of reflection first exceeds the critical angle. At that stage, the light exits the material. The position that the light exits the display will depend on the angles at which the light was projected into the planar light guide.
The planar light guide is used as a display device. In one case, the planar light guide is provided as a structure to perform X-ray imaging. X-rays that pass through an object are received at the planar light guide at the portion of non-uniform thickness. A film is positioned on the wedge portion where it is exposed to the X-ray light. Visible light, on the other hand, is directed along the inside of the planar light guide in the portion of relatively uniform thickness by the principles of total internal reflection. The visible light is then captured by a camera positioned at the edge of the planar light guide. However, the planar light guide is not used in an interactive display that integrates both display and imaging functionalities.